This invention relates to a contactlessly operating electronic responder card comprising an electronic circuit incorporated into the card and an antenna coil incorporated into the card.
Contactlessly operating responder cards of the type described above also referred to as "chip cards" are known per se, for instance from DE-C-3721822 and from NL-A-9100176, and can be used for a variety of purposes. Possible applications include the use as identity card, bank pass, admission card, identification label, credit card, telephone card etc. Since such cards, labels or passes often represent a non-negligible (money) value, such cards etc. are generally, and also hereinafter, designated by the term value document.
A problem in the manufacture of a value document of the above-described type is that the value document should be thin and slightly flexible to satisfy the requirements to be met in normal use. However, an antenna coil, and particularly an antenna coil that covers a great portion of the surface of the value document, is difficult to manufacture or to integrate into the value document in such a manner that the antenna coil does not adversely affect the desired flexibility and the desired minor thickness dimension of the value document. A relatively large antenna coil is required if data transmission between the card and a transmitter/receiver at a relatively large distance of, for instance, more than 50 cm is desired, and particularly if the value document should be able to function without a battery of its own.
In known coil constructions, the following main principles can be distinguished. 1) A rigid coil construction on the basis of a so called coil bobbin, which is a form-determining part around which the wire is wound. 2) A coil construction utilizing so called thermoadhesive wire, in which the windings are stuck to each other at an increased temperature by means of an adhesive layer. 3) A coil construction in which a form-retaining wire of such thickness is used that the form of the coil is thereby retained.
The drawbacks of the known coil constructions for use in a value document are the limited flexibility, or the space required, as well as the influence of the material of the coil on the form of the value document, which, for instance, manifests itself inter alia in flatness and form retention in the case of fluctuations in the temperature. The object of the invention is to realize a flexible coil construction which does not have the above-mentioned drawbacks, and which is generally suitable for use in a thin and flexible value document of the above-described type.